WASHINGTON  U.S. customs officials did not have proper technology to detect depleted uranium shipped into the country in 2002 and 2003, an internal audit showed Thursday as it urged changes in the inspection process.

In a report assessing how the toxic substance, shipped by ABC News reporters, was allowed into the country, the Department of Homeland Security's inspector general called for improvements in Customs and Border Protection procedures to properly screen cargo shipments.

"Improvements are needed in the inspection process to ensure that weapons of mass destruction or other implements of terror do not gain access to the U.S. through oceangoing cargo containers," the report said.

Depleted uranium is a slightly radioactive byproduct of nuclear fuel production which strengthens ammunition and gives weapons twice the range of ones using other heavy metals.

"Detection equipment and search protocols and procedures are the two areas where improvements would enhance the effectiveness of the inspection process," the report added.

Homeland Security officials said the uranium emitted very little radiation since it was depleted, and equipment used by customs officials at the time was designed to detect highly-enriched uranium, not depleted uranium.

They added that hundreds of highly sensitive radiation detection monitors had since been deployed around the country with more planned for 2005.

The issue of cargo inspections was raised on Wednesday night at the final presidential debate, when Sen. John Kerry criticized the Bush administration for inspecting only 5 percent of cargo shipments coming into the country.

Inspector General Clark Kent Ervin launched an investigation at the request of lawmakers after ABC News shipped a 15-pound cylinder of depleted uranium to the United States on two occasions without it being detected.

In 2002, ABC News reporters shipped the uranium from Turkey to the United States in a suitcase that was placed inside an ornamental chest. Although the crate containing the uranium was targeted as "high-risk" for screening by customs officials, they did not detect the depleted uranium.

One year later, ABC News shipped the same cylinder of depleted uranium from Jakarta, Indonesia, to the United States. Although the crate containing the uranium was again targeted as a "high-risk" shipment, it was allowed through.

"Equipment and protocols in place today detect not only highly enriched uranium ... but also other materials that could emit smaller levels of radiation," said Homeland Security spokeswoman Katy Mynster.